Wood is an important natural resource and forms the basis of many of today's modern products. However, once trees are harvested and cut into logs, they usually need to be further processed prior to their end use. For example, in the pulp or oriented strand board industries, one often needs to pass the log through a machine which turns the solid log into a plurality of chips or wafers respectively. Such machines are typically referred to as chippers, which may be in a disk form, or a drum form, and waferizers, which also take a number of forms. In the sawmill industry, logs or semi-manufactured lumber are commonly passed through machines which chip or plane away the outside portions of the solid log or semi-manufactured lumber to transform the wood into finished lumber and a plurality of wood chips. Such machines are typically referred to as planers, chipper canters, chipper edgers, and chipper slabbers each which can take a number of different forms.
One of the objects of such chipping machines is to produce chips of wood that are generally of an even size and to produce such chips with a low amount of excessively small, thin, thick or oversized fractions that may be detrimental to their particular end use. For example, chips of an even size help facilitate further processing of the wood in the production of pulp. Having chips of an even size means that process controls can be established which result in a homogeneous treatment of the chips in the process. Since too many large sized chips or too many small sized chips can affect the quality of the output, wood chips are traditionally separated for size by screening with only the acceptable fraction being employed in the pulping process. The excessively small, thin, thick, or oversized fractions are removed and are often discarded or reprocessed. As a result, maximizing the amount of processed wood which is in the desired chip size while producing a minimum amount of reject material maximizes the efficient use of the wood. It is a similar goal of waferizing apparatus to produce wafers or strands of uniform size as well.
In lumber production, one of the objects of chipper canters, chipper edgers, chipper slabbers and planers is to produce lumber with a uniform and accurate cut surface. For example, an accurate cut surface allows for the production of lumber closer to targeted dimensions and of more uniform size. Having a more accurate control over lumber dimensions means that a more preferable cut location can be adopted allowing for a more efficient use of the wood.
Chippers and waferizers are typically large machines that include rotating disks or rotating drums equipped with a plurality of knives. More recently, chippers have included indexable knives such as shown in our earlier patents, Canadian Patent 1,201,695, and U.S. Pat. Nos. 4,047,670, and 5,348,065. Similarly, chipper canters, chipper edgers, chipper slabbers, and planers are machines that include rotating chipping heads or rotating planing heads of general cylindrical or conical profile equipped with a plurality of knives.
In many of the aforementioned machines, indexable or rotatable knives are preferred, because essentially, two or more knife edges can be provided on a small high quality knife element permitting increased operating efficiency and ease of use. However it will be appreciated, by those skilled in the art, that larger old style non-indexable type knife elements are also commonly in use.
In indexable knife arrangements, the knife element is commonly provided with a profile which is gripped between an upper and lower clamping surface. The upper and lower clamping surfaces hold the knife element in place while the knife element is directed onto the wood being processed. As such, the clamping assembly typically includes an upper clamping component, a lower clamping component and a bolt or a plurality of bolts to clamp the clamping components together. There may also be an associated adapter or adapters to hold the clamping assembly described above in place on a rotating disk, drum, or hub.
While such devices are very efficient in holding knives in place, by allowing the knife elements to be released and either rotated or replaced in the clamping assemblies, there are certain problems that are associated with them. One of the problems is to ensure that the knife edge is accurately positioned within the knife clamping assembly. What is desired in all cases, in order to produce chips of an even size, wafers of uniform dimensions, or lumber of accurately cut surface, is that the knife edge of the knife element be positioned at exactly the right distance relative to the machine. For example, in waferizing apparatus accurate positioning of the knife edge means that the wafers can be more precisely formed of the same size. In this respect, it will be understood by those skilled in the art that for a consistent wafer thickness to be achieved a precise knife projection above the drum or disk surface is required, and that even a small displacement of a knife edge, relative to the drum or disk surface could result in a different sized wafer being formed. Therefore, it is desirable to have the knife edge positioned with the highest precision possible relative to the spinning knife drum or disk.
Even with recent advances with indexable knives, the knife elements usually still need to be frequently replaced or rotated. Recent improvements to the design of knives and clamping assemblies can permit such knife replacements to be done efficiently and relatively easily by one or two workers. However, it is not always possible to position the rotation of the disk, drum, or hub such that the knife element being replaced or rotated is in an ideal position to be worked on. In some cases the workers may be reaching overhead, or around cumbersome components to make the change. Thus, it can be difficult to precisely position the knife element in the clamping assembly under such awkward circumstances. Further, each of the clamping components and knife elements must be built to certain tolerances. The smaller or tighter the tolerances the higher the costs typically associated with their manufacture. By reason of such tolerances there can be a resulting range for the location and orientation of the knife element within the clamping assembly. Generally, the larger the clamping assembly and knife element, the larger will be the corresponding set of tolerances, and potentially, more varied the fit. In practice, the combination of manufacturing tolerances and an awkward working environment conspire together to adversely affect precise knife edge positioning.